I20 



SCIENCE. 



[Vol. XV. No. 368 



degrees in tbe leai-. In this pcsilior, live steam is admitted from 

 the ma'n steam-pipe a (Fig. 3), thence through poits b', pipe a', and 

 port g", to cylinder H"; und at the same instant steam which has 



(Fig. 3), pipe a", and port g'" (Figs. 1 and 3), to cylinder H". At 

 this point aUo, piston H', moTing upward, closes the connection 

 between cylinders H' and L". and the steam expands in L" fcr 

 the remainder of the strolie. As piston L" reaches the lower 

 centre, port cl (Fig. 1) comes opposite pipe e', and the exhaust 

 steam passes through this connection into pipe e (Fig. 4), which 

 communicates with the atmosphere or condenser. When piston 

 H' reaches the upper centre, live steam passes from a (Fig. 3) 

 through port 6", pipe o'", and port g', to cylinder H', and the 

 partly expanded steam passes from cylinder S" down through 

 port g'" (Fig. 1) and pipe e " to cylinder L'. Cylinder L'" exhausts 

 through pipe e" and port d" into e, and cylinder L' through pipe 

 e'" and port d'" into e. 



The valve X (Fig. 3) is merely a live-steam connection with the 

 low-pressure cylinders for heating up and starting. Thus, with 

 the exception of the cut-off, each set of pistons controls the steam in 

 the cylinder next preceding, in the order of rotation, and, when 

 acting as a valve, is at or near its maximum speed; while the pis- 

 tons in the preceding c} linders are at or near their slowest speed. 

 This simple expedient controls the steam in this engine in a man- 

 ner unexcelled by any valve device. 



All lubrication is automatic, consisting of a sight-feed lubricator 

 on the steam-pipe, a drop-sight-feed cup on each end-beaiing of 

 the shaft, and a mi-^ture of oil and water in the crank-case, per- 

 fectly lubricating all parts within. The cylinders are cast in one 

 piece, and bored at the same time on a tool especially designed for 

 the purpose, by which means they are made absolutely parallel, 

 and the danger of leaky joints is avoided. The bearings for the 

 shaft are bored oat after being bolied in place, insuring perfect 

 alignment; and all wearing surfaces are exceptionally large, so 

 that internal friction is reduced to a minimum. The only adjust- 

 ments consist of two keys in the connecting-rods, which take up 

 all the wear in both boxes. The pressure being always down- 

 wards, these adjustments are seldom necessary; and the engine, 

 it is claimed, will run indefinitely without stoppage, and with but 

 little attendance. 



been partly expanded in cylinder H passes down through port g' 

 (Figs. 1 and 3) and pipe e', to cylinder L", thus admitting live and 

 low-pressure steam on one set of pistons at the same moment. Un- 

 der the action of the steam, pistons H" and L" move downward, 



THE TENSILE STRENGTH OF SHEET ZINC. 



So little has been published about the strength of zinc, that any 

 contribution to this question must be welcome. The most care- 

 ful tests -which Professor Martens made on some zinc sheets sup- 

 plied, by the Schlesische Actien-Gesellschaft ftir Bergbau und 

 Zinkhiittenbetrieb at Lipiue, in Silesia, on behalf of these works, 

 hence, deserve all the more attention. These tests, according to 

 Engineering of Jan. 81, were caiTied out at the Eoyal Technical 

 Testing Station at Berlin, of the mechanical department of which 

 Professor Martens is chief, and are describeel in the official re- 

 ports of that institution, 1889, IV, 



The reputation of zinc as a stmctural material is not particu- 

 larly good, anel these tests do not tend to show that the metal de- 



live. steam being admitted until the upper edge of port g" (Fig. 1) 

 passes the lower edge of pipe a', at which point it is cutoff, and 

 expands in this cylinder until the lower edge of port g" passes the 

 upper edge of pipe e", at which point it passes to cylinder L'". At 

 the same moment live steam passes from a through port 6' 



serves a better name for constancy and reliability of its mechani- 

 cal properties. A gi-eat many tests had to be made to arrive at 

 fair averages . The test samples were five sheets, supplied by the 

 Silesia mills of the above works, two specimens from foreign 

 works ; and finally eleven sheets rolled before Professor Martens 



